Development of effective vaccines against respiratory viruses requires a thorough understanding of the immunological response to individual proteins. For this reason panels of recombinant vaccinia viruses expressing individual influenza A, respiratory syncytial (RS), and paramyxovirus SV5 proteins were constructed. In the case of influenza, a complete set of 9 recombinant viruses were made. For respiratory syncytial virus and SV5, recombinants expressing the 2 envelope proteins were prepared. In all cases the synthesized polypeptides closely resembled the natural ones with regard to electrophoretic mobility, antigenicity, and intracellular transport. The recombinant vaccinia virus expressing HA was most effective at protecting mice against respiratory influenza infection. Cottons rats were protected against RS virus most effectively with the recombinant expressing the F protein although considerable protection also was obtained with the G recombinant. By contrast, cottons rats were better protected from SV5 infection with the vaccinia expressing HN than with vaccinia expressing F, although the latter induced even higher levels of neutralizing antibody. The ability of all of the recombinant vaccinia viruses to induce cell mediated immunity and to serve as cytotoxic T cell targets was measured.